Authentication flow in Spring Boot - Step-by-Step Execution

Concept Flow - Authentication flow

User submits login form

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Spring Security intercepts request

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AuthenticationManager checks credentials

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Create [Reject login

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Set Security Context

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Allow access to protected resource

This flow shows how Spring Boot handles user login: user submits credentials, system checks them, then grants or denies access.

Execution Sample

Spring Boot

POST /login with username and password
AuthenticationManager.authenticate(token)
If success, SecurityContextHolder.getContext().setAuthentication(auth)
Return success response
Else return error

This code handles a login request by checking credentials and setting the user as authenticated if valid.

Execution Table

Step	Action	Input	Result	Next Step
1	User submits login form	username=alice, password=1234	Request received	2
2	Spring Security intercepts request	Login request	Authentication token created	3
3	AuthenticationManager authenticates	Token with credentials	Credentials valid?	4
4	Check credentials	username=alice, password=1234	Yes	5
5	Create Authentication object	User details	Authentication created	6
6	Set Security Context	Authentication object	User marked authenticated	7
7	Return success response	Authenticated user	Access granted	END
8	If credentials invalid	Invalid password	AuthenticationException thrown	Return error response

💡 Execution stops after success response or error response is returned

Variable Tracker

Variable	Start	After Step 2	After Step 3	After Step 5	After Step 6	Final
username	null	alice	alice	alice	alice	alice
password	null	1234	1234	1234	1234	1234
authenticationToken	null	created	created	created	created	used
authentication	null	null	null	created	set in context	set in context
securityContext	empty	empty	empty	empty	holds authentication	holds authentication

Key Moments - 3 Insights

Why does Spring Security create an Authentication token before checking credentials?

The token holds the user input securely and standardizes the data format for the AuthenticationManager to process, as shown in step 2 and 3 of the execution_table.

What happens if the credentials are invalid?

An AuthenticationException is thrown and the flow jumps to returning an error response, as shown in step 8 of the execution_table.

Why do we set the Authentication object in the Security Context?

Setting it marks the user as authenticated for the current session, allowing access to protected resources, as shown in step 6.

Visual Quiz - 3 Questions

Look at the execution_table, what is the state of 'authentication' after step 5?

A Authentication token is created

B Authentication object is null

C Authentication object is created

D Security context is set

💡 Hint

Check the 'Result' column at step 5 in the execution_table

At which step does Spring Security decide if credentials are valid?

A Step 2

B Step 4

C Step 3

D Step 6

💡 Hint

Look at the 'Action' and 'Result' columns around steps 3 and 4 in the execution_table

If the password is wrong, which step shows the flow handling this?

A Step 8

B Step 7

C Step 5

D Step 6

💡 Hint

Check the row mentioning 'AuthenticationException' in the execution_table

Concept Snapshot

Authentication flow in Spring Boot:
1. User submits login form.
2. Spring Security creates an Authentication token.
3. AuthenticationManager checks credentials.
4. If valid, sets Authentication in Security Context.
5. Grants access; else returns error.
This flow secures protected resources by verifying identity.

Full Transcript

In Spring Boot, when a user submits a login form, Spring Security intercepts the request and creates an Authentication token holding the credentials. The AuthenticationManager then checks these credentials. If they are valid, an Authentication object is created and set in the Security Context, marking the user as authenticated. The system then grants access to protected resources. If credentials are invalid, an exception is thrown and an error response is returned. This flow ensures only authenticated users can access secured parts of the application.